High-power diode lasers are used in many different applications. The usefulness of a laser for a specific application can be characterized by the laser's output power, the spectral line width of the output light, and the spatial beam quality of the output light. The spatial beam quality can be characterized in several ways. For example, a wavelength independent characterization of the spatial beam quality is provided by the beam parameter product (“BPP”), which is defined as the product of the beam waist, ωo, and the half far-field divergence angle of the beam, θo, (i.e., BPP=ωoθo). As another example, a dimensionless characterization of the spatial beam quality is provided by the beam quality factor, M or Q, where, M2=1/Q=πωoθo/λ, with λ being the wavelength of the output laser light.
Different applications require tailoring the laser's output power, spectral line width, and spatial beam quality in different ways that optimize system performance. For example, high power output from a semiconductor diode laser can be achieved using a relatively wide lateral width of the active material. Such devices may be known as “wide stripe emitters,” broad stripe emitters,” or “multimode devices.” However, when the lateral width of the active material is greater than several times the laser output wavelength, gain can occur in higher order spatial modes of the resonant cavity, which can reduce the spatial beam quality of the output laser light. Multiple wide stripe emitters can be fabricated side-by-side on a single chip to a make an array of diode lasers. The output light of multiple individual diode lasers in an array can be combined incoherently to increase the overall output power from the chip. However, the quality of the combined output beam generally decreases with the number of individual emitters in an array.